Cardiovascular diseases remain the major cause of death in the US. Stem and progenitor cell- derived cardiomyocytes (SPC-CMs) hold great promise for myocardial repairs. Recent progress in cellular reprogramming of various somatic cell types into induced pluripotent stem cells (iPSCs) opened the door for developing patient-specific, cell-based therapies. However, most SPC-CMs displayed heterogeneous and immature electrophysiological (EP) phenotypes with uncontrollable automaticity. The characteristics and stages of differentiation of cardiomyocytes (CMs) derived from SPCs or iPSCs need to be clearly defined before a safe clinical application could be performed. Furthermore, iPSC technology enables the creation of stem cell lines from patients with known genetic diseases, which has been used to study disease pathogenesis and to design therapy. In this proposal, we plan to create methods of inducing maturation of SPC- or iPSC-CMs by co-culturing endothelial cells (ECs) with these primitive CMs. We have identified that ECs promote Na+ channel expression of primitive CMs via endothelin-1 pathway. Also, we have created 3 human iPSC lines that could differentiate to CMs. We further generated the first cardiac disease-specific iPSC line that produced CMs with pathological signatures of arrhythmogenic right ventricular dysplasia (ARVD). Furthermore, we created human embryonic stem cell (hESC) and iPSC lines with Puromycin resistance by lentiviral vectors to allow rapid isolation of >95% pure iPSC- or hESC-CMs for genetic and EP analysis. Finally, in order to clearly identify the nature and fate of these normal and diseased iPSC-CMs, we have started to generate an extensive genetic map of 6 regions of embryonic and adult human hearts by micro- array technologies. Using bioinformatic analysis of data from genetic arrays, we will create a comprehensive dataset, termed Developmental HeartMatrix, so that we could compare characteristics of iPSC- or SPC-CMs to those of CM subtypes from various stages of human hearts during development, as well as to determine the stages of iPSC-CM differentiation. This project, if completed, will provide the genetic signature maps to develop methods of inducing maturation of primitive iPSC-CMs toward appropriate CM subtypes for a safe cell-based therapy. Most importantly, a human ARVD in vitro disease model could be generated by iPSC technology as the foundation for developing clinical therapy.